Manufacture of white lead



' 30 chosen in such a way Patented July 12,1927.

UNITED STATES.

' MELBOURNE, VICTORIA, AUSTRALIA, ASSIGNORS T COMMONWEALTH WHITE LEADAND PAINTS PROPRIETARY LIMITED, OF MELBOURNE, AUSTRALIA.

MANUFACTURE 01 WHITE 80 Drawing. Application filed August 8,

Experiments in the production of highly basic lead salts (i. e.containing a high per- 'centage of lead hydroxide,) suitable for themanufacture of white lead have convinced us I that one of the mostsuitable salts for all practical purposes is the basicsulphate.

According to the presentinvention therefore we treat lead monoxide withwater and a: small quantity of acetic or other suitable 1 acid (e. g.nitric) to ensure the presence in the mixture of a certain amount oflead in water soluble form to facilitate the subsequent sulphatingaction. This mixture is brought to a suitable temperature and treatedwith concentrated sulphuric acid. If necessary to maintain a workableconsistency more water is added to the mixture towards the end of thesulphating process. The reaction proceeds most smoothly when the mixtureis ground during the whole of this stage in the manufacture. t

The basic sulphate is treated in. the cold with a; mixture of a solublebicarbonate of an alkali metal and water preferably in the form of aslurry there being undissolved; carbonate present, and reaction occurswhich re sults not merely in the displacement of the sulphate radiclebut inthereduction of the basicity and our proportions of reagents arethat the white lead has a composition cal (31.1% lead ydroxide).

' The acid sulphates of the alkali metals can be substituted forequimolecular proportions of sulphuric acidwith satisfactory results,

that is to say not less than 26% parts of potassium acid sulphate normore than 42% parts or alternate y not less than 23 nor more than 37parts of sodium acid sul 40 phate for each 112'partsof lead monoxide.-

In order that the composition of the white lead'may approximate thetheoretical it is necessaryv that the proportion of water present duringsulphatmg shall not be less than nor more. than 2 parts by weight foreach 1 part of litharge treated,

The temperature obtalning during the formation of the basic sulphate hasa con- 'siderable influence upon its hysical properties. Unless itexceeds 40 the'reaction is inconveniently slow and if it is permitted torise from this temperature too ra Unless t e directions as to limits oftemapproximating to the theoretiidly the basic sulphate sets in anintracta 1e mass.

1924, Serial no. 730,937, aim in Australia August'm, 1923. A

.perature -indicated are observed a basic sulphate is obtained which isapt to contain unchanged litharge admixed with a sulphate the basicityof which is not as high 'a'sthat almed at. Such. a mixture on beingcarbonated gives rise to a white lead of inferior colour and containingtoo small a percentage of hydroxide.

The composition of the product depends upon two principal factors namelythe proportions of sulphuric acid andsodium .bi-

carbonate and, according to our invention we- PATENT -.0FFICE.

GEORGE FREEMAN LLOYD, 'OF ERIeR'roiI, AND FREDERICK HAR'RER CAMPBELL, or

impurities. The limits between which the proportions of the reagentsnamed can be varied are accordingly not widely separated and we findthat for each 112 parts of litharge the amount of concentrated (96%)sulphuric acid should be between 10 and 16 parts by weight and thesodium bicarbonate between 27 and 30 parts by weight.

.We do not claim any particular proportion of acetic acid, but find thatfrom 1 to 2 parts of 30% acid for 112 parts of litharge are suitableamounts.

If desired a mixture of sodium bicarbonate and sodium carbonate may beused for converting the basic sulphate to basic carbonate, in theapproximate ratio of 2 to 1. A

Without'limiting the scope of our invention the followin exam le isillustrative of its practical wor 'ng: e take 112 lbs. of litharge freefrom red lead and substantially free from metallic lead, mix with itlbs. of warm water and 2 lbs. of 30% acetic acid. The mixture'is heatedto about 40 C., by blowing in steam, or by other suitable means, whilebein ground in a Chilean mill or other suitable evice. Twelve pounds ofsulphuric acid (96%) is. introduced in the form of a thin stream, therate being determined by thetem erature, which should not risematerially a ve 150 C. When the greater part (say g lbs.) of thesulphuric pound i o :1

acid has been added about 20 lbs. of water is introduced and then therest of the acid. We convert the basic sulphate into basic carbonate bythe addition of lbs. of sodium bicarbonate previously mixed with 80 lbs.of cold Water. After completion of the action, under the influence ofgrinding, the material is washed with water and dried, or mixed with oiland ground.

We claim:

1. The manufacture ct white lead which comprises mixing 13.12 lbs. oflead m xide tree from red d end substaniia" water and an acid capableoil? formii'ig w soluble lead salts equivalent to abo twug and one-halfpounds of 30% acetic acid heating the mixture to about 40 C whilegrinding, introducing an acid sulphatmg Fix a cut equal to about 12pounds of 96% sulp uric acid in a tlliin stream with about 20 W-*?ter,convertin the basic sulphate time formed into basic carbonate by theaddition of an alkali metal carbonating reagent equ 'valent to not lessthan 27 nor more than 30 of sodium bicarbonate preriously mixed withabout 80 lbs. of cold LBSBJZWH water under the influence of grinding,and

Washing and drying the resultant basic carbonate.

2. in the manufacture of white lead, the step which comprises reactingupon 112 parts of lead monoxide with a sulphating reagent equival nt to10 to 16 parts of concentrated sulphuric acid in the presence of a smallquantity of an acid capable of forming Water soluble lead salt, andWater the propor lion of not less than one-half and not more than twoparts of Water for each part of lead monoxide treated.

3 In the manufacture of white lead, the step of converting the basicsulphate of lead nr ritaining from 60 to 76.50 per cent of lead 1 doxide into basic carbonate of lead containing approximately 30 percent'of lead nydroxide which comprises reacting on such sulphate with analkali metal carbonating reagent equivalent to not less than 27 nor morethan 30 parts of sodium bicarbonate and suflicient water for such agentto be partly in suspension and partly in solution. Dated this sixteenthday of mm 1924.-

csoacs mama LLOYD. mower mares cmram.

